This invention relates to a pad for providing topical heat and in particular to a self-contained warming pad for conveniently providing a source of heat which can be used in situations where heat sources are normally inaccessible.
The prior art includes disclosures of heating pads of various types for use in a wide variety of applications. A number of such pads are designed for convenient use. For example, certain chemical pads include two exothermically reactive substances separated one from another within a plastic bag or the like. Such a heating pad may be activated by fracturing a separator (an internal container for an actuating liquid) and allowing intermixture of chemicals to provide heat. Other known heating pads utilize an electrochemical element of the type described by Kober in U.S. Pat. No. 3,774,589. These pads, which may be activated by the addition of water or an electrolyte solution from outside the pad, have been successfully utilized commercially. These and other known heating pads have substantial disadvantages in certain applications.
The prior art heating pads including the self-contained heating pads (that is, those containing all necessary energy and/or material for activation) do not provide a convenient form of heat for specific applications such as the warming of hands during recreational or work activities in cold environments. Chemical heating pads are often rather difficult to activate and are normally too heavy for convenient portability, and too bulky and/or cumbersome for convenient use in such applications.
Other specific problems relate to difficulty in providing a controlled high temperature for extended durations in the activated heating elements for safe and effective topical use on human skin. In some pads peak temperatures are not controlled, giving rise to the risk of burns. In other pads, the temperature curve falls off rapidly such that effective heat is available only briefly.
Known electrochemical heating pads are not self-contained and require special activating procedures which are not viable in many applications. Thus, accessibility of an activating fluid poses a specific problem for the use of such pads as handwarmers and the like. Furthermore, adding activating fluid to an electrochemical heating element gives rise to concomitant problems relating to the amount and/or concentration of activating fluid used. These problems can include overheating, insufficient activation, wetting and the like.
The heat-producing potential of various pads, including certain pads using electrochemical heating elements, is often limited by the inaccessibility of air to the heat-producing site of such pads during operation. However, measures taken to allow a supply of air at the heat-producing site tend to open the pad cover, thus exposing to the outside or allowing the leakage of liquids. In other words, to optimize the heat-producing ability of a pad the human user might have to risk exposure of his skin to these liquids, with a possible attendant feeling of discomfort.
In summary, this invention addresses the need for a warming pad which is lightweight, limited in size and bulk, conveniently activated, safe is use, self-contained, and capable of providing substantial surface temperatures and delivering substantial heat for sustained periods, that is, a heating pad for convenient, reliable topical use in specific applications such as the warming of hands in recreational or work activities in cold environments.